Dr. Jason Block is a general internal medicine physician committed to a research career focused on innovative interventions to combat obesity. This K23 Research Career Development Award will build upon his strong methodological skills obtained during a recently-completed population health research fellowship. With support from the K23, he will gain additional skills in advanced epidemiology, economics, qualitative research, analysis of quasi- and natural experiments, and randomized controlled trials. The goal of this K23 is for Dr. Block to learn these skills through coursework, mentorship and the practical application of these skills in Aims that evaluate workplace wellness initiatives to promote a healthy weight. Mentors with expertise in epidemiology, nutrition, biostatistics, behavioral economics, and economics will guide training and research for Dr. Block, and each mentor will meet with him at least monthly to provide training, feedback on projects and assessments of his career development. Dr. Block's department has a long history of supporting junior faculty members and developing them into independent investigators. The department will unequivocally protect 75% of Dr. Block's time for research during the K23 award period and will continue to provide institutional resources to support his work. The need for novel interventions to address the obesity epidemic in the US is the motivation for the Aims of Dr. Block's K23 proposal. Sustaining a healthy weight can be difficult because of the ubiquitous availability of low- cost, unhealthful foods and physiologic mechanisms that counteract weight maintenance. Intensive individual- level interventions, using behavioral counseling and educational initiatives that target one individual or a small group of individuals at a time, can lead to sustained weight loss but are costly and difficult to implement broadly. Environmental interventions, such as the restructuring of the menu in a workplace cafeteria, and financial incentives promoting weight maintenance are two strategies that might overcome the obesogenic environment and the physiological barriers to sustained weight loss. Workplaces are logical sites for these interventions because Americans spend much of their waking hours at work, and employers could gain financial benefits from a healthier and more productive workforce, especially through low cost interventions. An environmental food services intervention is one cited example of a relatively inexpensive intervention. Workplaces, especially those with existing infrastructure such as occupational health clinics and on-site primary care clinics, also are ideal settings to carry out low-cost, behavioral trials. Dr. Block proposes to evaluate two workplace wellness initiatives to reduce risk for overweight and obesity and to promote weight maintenance within Brigham and Women's Hospital, a large academic medical center in Boston, Massachusetts, with nearly 16,000 employees. The Aims are 1) to conduct focus groups among Brigham and Women's employees to gather their views on workplace wellness initiatives, their response to the environmental intervention in the cafeteria, including new menu, and their reaction to our proposal for a deposit contract weight maintenance trial; 2) to examine the extent to which a new cafeteria menu influences the sales of healthy and unhealthy food and beverages, decreases the calorie content of employees' meals in the cafeteria, and decreases the total daily calorie, trans fat, and saturated fat intake of employees, and 3) to determine the extent to which a deposit contract improves weight maintenance among employees who have lost 10 lbs during the prior year. These initiatives incorporate common behavioral economics principles, including the large effect of defaults on behaviors and the power of loss aversion, which is the natural inclination to avoid losses or regret, in motivating behavior change. Through the training activities, mentorship, and research experience provided by the K23, Dr. Block will become a successfully independent investigator, exploring mechanisms to combat obesity among Americans.